1. Field of the Invention
The present invention relates to a control device for a walking assist device for assisting a user (person) in walking.
2. Related Background Art
Conventionally, the applicant of the present application proposed this type of walking assist device, for example, in Japanese Patent Application Laid-Open No. 2007-54616 (hereinafter, referred to as Patent Document 1) and Japanese Patent Application Laid-Open No. 2007-330299 (hereinafter, referred to as Patent Document 2).
These Patent Documents 1 and 2 disclose a walking assist device including a seat member on which a user is seated in a straddling manner, a pair of left and right foot attachment portions fitted to the left and right feet of the user, respectively, and a pair of left and right leg links interconnecting the seat member and the left and right foot attachment portions, respectively.
In this walking assist device, each leg link includes a thigh frame extending from the seat member via a first joint (hip joint), a crus frame extending from the foot attachment portion via a second joint (ankle joint), and a third joint (knee joint) that interconnects the thigh frame and the crus frame so that the frames freely bend and stretch between the first joint and the second joint. Moreover, an electric motor for driving the third joint is mounted at an end of the thigh frame on the first joint side of each leg link. Further, in this walking assist device, in a state where the foot attachment portion is in contact with the ground, the electric motor applies a driving torque to the third joint of the leg link in the stretching direction of the leg link. This causes a lifting force to be applied to the user from the seat member and consequently the walking assist device bears a part of the weight of the user.
In this instance, the walking assist device controls the motion thereof as described below. Specifically, a desired total lifting force as a total supporting force (translational force), which is required to support a part of the weight of the user and the weight of the walking assist device on the floor, is distributed to the leg links at a ratio based on the treading forces of the legs of the user measured from the outputs of treading force measurement force sensors provided on the foot attachment portions. This determines the desired values of the supporting forces applied to the leg links from the floor side (the desired shares of the leg links of the desired total lifting force). In this case, the desired values of the supporting forces of the leg links are determined so that the mutual proportion between the desired values of the supporting forces of the left and right leg links is the same as the mutual proportion between the treading forces of the left and right legs of the user. Moreover, supporting forces actually acting on the leg links from the floor side are measured from the outputs of force sensors, each of which is interposed between the crus frame and the second joint of the corresponding leg link. Further, an output torque of the electric motor is feedback-controlled for each leg link so that a measured value of the supporting force coincides with the desired value. This allows the output torque of each electric motor to be controlled so that the desired lifting force acts on the user (a translational force supporting a part of the weight of the user) from the seat member.
In the walking assist device mentioned above, force at each leg link is generated so as to conform to the treading forces of each of the legs of the user, that is, the motion of the leg the user intends, so that the burden of the leg during the user walking or the like may be reduced effectively.
In the technique disclosed in the Patent Documents 1 and 2, it is necessary to have a plurality of treading force measuring force sensors for measuring the treading forces of each of the legs of the user, as well as an A/D converter for each of the treading force measuring force sensors in order to A/D convert the outputs thereof. Therefore, the production cost of the walking assist device is likely to increase.
Further, the output of each treading force measurement force sensor tends to change with a slight movement of the foot attachment portion upon landing. Therefore, there are cases when the mutual proportion of the treading forces of the left and right legs of the user instantaneously changes by the slight movement of the foot attachment portion upon landing. In such case, an instantaneous variation in the mutual proportion of the desired value of the supporting force of the left and right leg links is generated. Consequently, there is a fear that the behavior of the walking assist device becomes inappropriate for the behavior desired by the user.